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author | Vitaly Kuznetsov <vkuznets@redhat.com> | 2015-03-27 09:10:13 -0700 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-04-03 16:18:02 +0200 |
commit | 0a1a86ac046091d7228c9f3a283dea5be96275dd (patch) | |
tree | cf4eca600c160ec8a00cbdd4f24794e246e0d822 /drivers/hv/hv_balloon.c | |
parent | 7fb0e1a65075a871c58cbcf8c877d1f9ae5cd83c (diff) | |
download | linux-stable-0a1a86ac046091d7228c9f3a283dea5be96275dd.tar.gz linux-stable-0a1a86ac046091d7228c9f3a283dea5be96275dd.tar.bz2 linux-stable-0a1a86ac046091d7228c9f3a283dea5be96275dd.zip |
Drivers: hv: hv_balloon: survive ballooning request with num_pages=0
... and simplify alloc_balloon_pages() interface by removing redundant
alloc_error from it.
If we happen to enter balloon_up() with balloon_wrk.num_pages = 0 we will enter
infinite 'while (!done)' loop as alloc_balloon_pages() will be always returning
0 and not setting alloc_error. We will also be sending a meaningless message to
the host on every iteration.
The 'alloc_unit == 1 && alloc_error -> num_ballooned == 0' change and
alloc_error elimination requires a special comment. We do alloc_balloon_pages()
with 2 different alloc_unit values and there are 4 different
alloc_balloon_pages() results, let's check them all.
alloc_unit = 512:
1) num_ballooned = 0, alloc_error = 0: we do 'alloc_unit=1' and retry pre- and
post-patch.
2) num_ballooned > 0, alloc_error = 0: we check 'num_ballooned == num_pages'
and act accordingly, pre- and post-patch.
3) num_ballooned > 0, alloc_error > 0: we report this chunk and remain within
the loop, no changes here.
4) num_ballooned = 0, alloc_error > 0: we do 'alloc_unit=1' and retry pre- and
post-patch.
alloc_unit = 1:
1) num_ballooned = 0, alloc_error = 0: this can happen in two cases: when we
passed 'num_pages=0' to alloc_balloon_pages() or when there was no space in
bl_resp to place a single response. The second option is not possible as
bl_resp is of PAGE_SIZE size and single response 'union dm_mem_page_range' is
8 bytes, but the first one is (in theory, I think that Hyper-V host never
places such requests). Pre-patch code loops forever, post-patch code sends
a reply with more_pages = 0 and finishes.
2) num_ballooned > 0, alloc_error = 0: we ran out of space in bl_resp, we
report partial success and remain within the loop, no changes pre- and
post-patch.
3) num_ballooned > 0, alloc_error > 0: pre-patch code finishes, post-patch code
does one more try and if there is no progress (we finish with
'num_ballooned = 0') we finish. So we try a bit harder with this patch.
4) num_ballooned = 0, alloc_error > 0: both pre- and post-patch code enter
'more_pages = 0' branch and finish.
So this patch has two real effects:
1) We reply with an empty response to 'num_pages=0' request.
2) We try a bit harder on alloc_unit=1 allocations (and reply with an empty
tail reply in case we fail).
An empty reply should be supported by host as we were able to send it even with
pre-patch code when we were not able to allocate a single page.
Suggested-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/hv/hv_balloon.c')
-rw-r--r-- | drivers/hv/hv_balloon.c | 19 |
1 files changed, 6 insertions, 13 deletions
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c index 4f5323cedab3..74312c88534a 100644 --- a/drivers/hv/hv_balloon.c +++ b/drivers/hv/hv_balloon.c @@ -1081,9 +1081,9 @@ static void free_balloon_pages(struct hv_dynmem_device *dm, -static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages, - struct dm_balloon_response *bl_resp, int alloc_unit, - bool *alloc_error) +static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages, + struct dm_balloon_response *bl_resp, + int alloc_unit) { int i = 0; struct page *pg; @@ -1104,11 +1104,8 @@ static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages, __GFP_NOMEMALLOC | __GFP_NOWARN, get_order(alloc_unit << PAGE_SHIFT)); - if (!pg) { - *alloc_error = true; + if (!pg) return i * alloc_unit; - } - dm->num_pages_ballooned += alloc_unit; @@ -1140,7 +1137,6 @@ static void balloon_up(struct work_struct *dummy) struct dm_balloon_response *bl_resp; int alloc_unit; int ret; - bool alloc_error; bool done = false; int i; struct sysinfo val; @@ -1173,18 +1169,15 @@ static void balloon_up(struct work_struct *dummy) num_pages -= num_ballooned; - alloc_error = false; num_ballooned = alloc_balloon_pages(&dm_device, num_pages, - bl_resp, alloc_unit, - &alloc_error); + bl_resp, alloc_unit); if (alloc_unit != 1 && num_ballooned == 0) { alloc_unit = 1; continue; } - if ((alloc_unit == 1 && alloc_error) || - (num_ballooned == num_pages)) { + if (num_ballooned == 0 || num_ballooned == num_pages) { bl_resp->more_pages = 0; done = true; dm_device.state = DM_INITIALIZED; |